An E-tree is a type of Ethernet virtual circuit (EVC for short) service defined by the Metro Ethernet Forum (MEF for short) organization. Specifically, the E-Tree has the following features: 1) A relationship between a root node to a leaf node is one-to-many, and a plurality of root nodes may exist; 2) an Ethernet frame of a root node may be sent to any root node and leaf node; and 3) an Ethernet frame of a leaf node may be sent to any root node, but the Ethernet frame of the leaf node cannot be sent to another leaf node, that is, a leaf node cannot be connected to, but needs to be isolated from, another leaf node.
A virtual private LAN service (VPLS for short) is a Layer 2 virtual private network (VPN for short) technology that is constructed on a Multiprotocol Label Switching (MPLS for short) network and used in a virtual Ethernet local area network. The VPLS technology enables users to access an MPLS network simultaneously from a plurality of geographically dispersed points and communicate with each other. Currently, a core network mainly adopts the Internet Protocol (IP for short)/MPLS technology. Therefore, there are more requirements of providing a virtual Ethernet service by using a VPLS, and the VPLS has been deployed quite widely. The VPLS can automatically discover a PE and construct a VPLS network by using the Border Gateway Protocol (BGP for short), which provides great convenience for creating a large-scale VPLS.
In an existing VPLS network, all provider edge (PE for short) devices are fully connected. Therefore, all Ethernet frames, no matter whether they are sent from a root node or a leaf node, reach all other root nodes and leaf nodes, which cannot accomplish effective isolation between leaf nodes supporting an E-Tree service. That is, the existing VPLS network cannot really implement a universal E-Tree service. Especially, when the existing BGP protocol is used for constructing a VPLS network, it is impossible to distinguish whether a customer edge (CE for short) device connected to a PE is a root node or a leaf node, and therefore, information streams between the leaf nodes cannot be restricted.